Cool stuff... :-)
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: J Morphol. 2006 Jul 18; [Epub ahead of print]
Postcranial pneumaticity: An evaluation of soft-tissue
influences on the postcranial skeleton and the
reconstruction of pulmonary anatomy in
archosaurs.O'connor PM.
Department of Biomedical Sciences, Ohio University,
College of Osteopathic Medicine, Athens, Ohio 45701.
Postcranial pneumaticity has been reported in numerous
extinct sauropsid groups including pterosaurs, birds,
saurischian dinosaurs, and, most recently, both
crurotarsan and basal archosauriform taxa. By
comparison with extant birds, pneumatic features in
fossils have formed the basis for anatomical
inferences concerning pulmonary structure and
function, in addition to higher-level inferences
related to growth, metabolic rate, and
thermoregulation. In this study, gross dissection,
vascular and pulmonary injection, and serial
sectioning were employed to assess the manner in which
different soft tissues impart their signature on the
axial skeleton in a sample of birds, crocodylians, and
lizards. Results from this study indicate that only
cortical foramina or communicating fossae connected
with large internal chambers are reliable and
consistent indicators of pneumatic invasion of bone.
As both vasculature and pneumatic diverticula may
produce foramina of similar sizes and shapes, cortical
features alone do not necessarily indicate
pneumaticity. Noncommunicating (blind) vertebral
fossae prove least useful, as these structures are
associated with many different soft-tissue systems.
This Pneumaticity Profile (PP) was used to evaluate
the major clades of extinct archosauriform taxa with
purported postcranial pneumaticity. Unambiguous
indicators of pneumaticity are present only in certain
ornithodiran archosaurs (e.g., sauropod and theropod
dinosaurs, pterosaurs). In contrast, the basal
archosauriform Erythrosuchus africanus and other
nonornithodiran archosaurs (e.g., parasuchians) fail
to satisfy morphological criteria of the PP, namely,
that internal cavities are absent within bone, even
though blind fossae and/or cortical foramina are
present on vertebral neural arches. An examination of
regional pneumaticity in extant avians reveals
remarkably consistent patterns of diverticular
invasion of bone, and thus provides increased
resolution for inferring specific components of the
pulmonary air sac system in their nonavian theropod
ancestors. By comparison with well-preserved exemplars
from within Neotheropoda (e.g., Abelisauridae,
Allosauroidea), the following pattern emerges:
pneumaticity of cervical vertebrae and ribs suggests
pneumatization by lateral vertebral diverticula of a
cervical air sac system, with sacral pneumaticity
indicating the presence of caudally expanding air sacs
and/or diverticula. The identification of postcranial
pneumaticity in extinct taxa minimally forms the basis
for inferring a heterogeneous pulmonary system with
distinct exchange and nonexchange (i.e., air sacs)
regions. Combined with inferences supporting a rigid,
dorsally fixed lung, osteological indicators of
cervical and abdominal air sacs highlight the
fundamental layout of a flow-through pulmonary
apparatus in nonavian theropods.
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1: Respir Physiol Neurobiol. 2006 Apr 30; [Epub ahead
of print]
On the origin of avian air sacs.Farmer CG.
Department of Biology, University of Utah, 257 South
1400 East, Salt Lake City, UT 84112, USA.
For many vertebrates the lung is the largest and
lightest organ in the body cavity and for these
reasons can greatly affect an organism's shape,
density, and its distribution of mass; characters that
are important to locomotion. In this paper
non-respiratory functions of the lung are considered
along with data on the respiratory capacities and gas
exchange abilities of birds and crocodilians to infer
the evolutionary history of the respiratory systems of
dinosaurs, including birds. From a quadrupedal
ancestry theropod dinosaurs evolved a bipedal posture.
Bipedalism is an impressive balancing act, especially
for tall animals with massive heads. During this
transition selection for good balance and agility may
have helped shape pulmonary morphology. Respiratory
adaptations arising for bipedalism are suggested to
include a reduction in costal ventilation and the use
of cuirassal ventilation with a caudad expansion of
the lung into the dorsal abdominal cavity. The
evolution of volant animals from bipeds required yet
again a major reorganization in body form. With this
transition avian air sacs may have been favored
because they enhanced balance and agility in flight.
Finally, I propose that these hypotheses can be tested
by examining the importance of the air sacs to balance
and agility in extant animals and that these data will
enhance our understanding of the evolution of the
respiratory system in archosaurs.
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Guy Leahy